1. Field of the Invention
The present invention is directed to a permanent magnet of the type SE--Fe--B that has the tetragonal phase SE.sub.2 Fe.sub.4 B as the principal phase, wherein SE is at least one rare earth element, including Y.
2. Description of the Prior Art
A magnet of the above general type is disclosed, for example, by in European Application 0 124 655 and in U.S. Pat. No. 5,230,751 that corresponds thereto. Magnets of the type SE--Fe--B exhibit the highest energy densities currently available. SE--Fe--B magnets manufactured by powder metallurgy contain approximately 90% of the hard-magnetic principal phase SE.sub.2 Fe.sub.14 B.
German Offenlegungsschrift 41 35 403 discloses a two-phase magnet, wherein the second phase can be a SE--Fe--Co--Ga phase.
European Application 0 583 041 likewise discloses a two-phase magnet, wherein second phase is composed of a SE--Ga phase.
U.S. Pat. No. 5,447,578 discloses a SE-transition metal-Ga phase.
Conventionally in the manufacture of these Se--Fe--B-magnets by combining Se--Fe--B base alloys with the composition close to the SE.sub.2 Fe.sub.14 B phase with a binder alloy with a lower melting temperature. The goal is thereby that the structure of the SE--Fe--B sintered magnets of SE.sub.2 Fe.sub.14 B base alloys is set with inter-granular binders, using optimally little binder alloy.
European Application 0 517 179 proposes the employment of binder alloys having the composition Pr.sub.20 Dy.sub.10 Co.sub.40 B.sub.6 Ga.sub.4 Fe.sub.rest (in weight percent, this is Pr.apprxeq.35, Dy.apprxeq.20, Co.apprxeq.28, B.apprxeq.0.77, Ga.apprxeq.3.5).
It has now turned out that the proportion of this binder alloy in the mixture of the base alloy must lie within 7-10 weight %. In this mixing range, sinter densities of approximately .rho.&gt;7.55 g/cm.sup.3 are achieved only at sintering temperatures above 1090.degree. C. These sinter densities roughly correspond to 99% of the theoretical density. Outside this mixing range, the sinterability, and thus the remanence that can be achieved are considerably influenced. The grain growth is highly activated in the magnets with a proportion of this binder alloy of more than 10 weight %, but the pores are not closed. The consequence is the formation of a structure with anomalously large grains (&gt;50 .mu.m) and with high porosity as well as with low sinter densities. Given lower proportions of binder alloy, the amount of the fluid phase is accordingly not adequate for the densification.